Semiconductor manufacture involves the formation of semiconductor devices on a semiconducting substrate. A large number of semiconductor devices or ICs are typically constructed on a wafer of single crystal silicon or gallium arsenide. The area on the wafer occupied by a discrete device or IC is called a die. After formation, the wafer is sawed into individual dies. Typically, each die is then packaged in a plastic or ceramic package which is recognizable as an IC chip.
Identifying data with respect to a particular die may sometimes be useful during the manufacture or life of the die. This data may include a date of manufacture, identification of a particular wafer from which a die was obtained, or identification of the location of a die on a wafer. Such information may be used for instance, to evaluate the performance characteristics of the die or IC chip.
In the past, this type of identifying data has been imprinted on the die, or on the outside of the packaged chip, using visual codes. A problem with a visual ID of a die is that a die is small and fragile and there is not much area available for an ID. In addition, after separation from a wafer, a die is subjected to many manufacturing steps that may damage and render a visual ID as unreadable. Moreover, a visual ID of a packaged chip may become unreadable during installation of the chip on a printed circuit board or during the life of the chip by an end user.
In view of the foregoing, there is need in the art for a method of identifying a semiconductor die, or other semiconductor structure, that is permanent and which is accessible during the manufacturing process and also during the subsequent life of a semiconductor chip. The present invention recognizes that a semiconductor die may be constructed with an integrated circuit that includes programmable links (i.e. fuses, anti-fuses, or programmable laser links), which may be used to create a code for identifying the semiconductor die.
Programmable links have heretofore been utilized in programmable semiconductor circuits. In general, programmable links are electrical interconnects that are either broke or created at selected electronic nodes to activate or deactivate the node. Such programmable links are widely used for instance, in programmable read only memory devices (PROMs).
The most common type of programmable link is a fuse. Fuses are typically formed of a material such as titanium tungsten alloy (TiW) formed in a bow-tie like shape (i.e. narrow neck, wide ends). If a sufficiently high voltage is applied to a fuse, the current flow will cause the fuse to heat up. This melts the neck of the fuse and causes the fuse to "blow" and create an open circuit.
PROM devices often include fuses which may connect a transistor or other electronic node to a lattice network. The PROM may be programmed by blowing the fuse to a selected node and creating an open circuit. A combination of blown and unblown fuses may thus represent a digital pattern of ones and zeros signifying data which a user wishes to store in the PROM.
Another type of programmable link used in programmable semiconductor circuits is called an anti-fuse. Anti-fuses, instead of causing an open circuit, create a short circuit or low resistance link. Anti-fuses typically include a pair of conductors having some type of dielectric or insulating material between them. The application of a predetermined voltage to the anti-fuse will break down the dielectric material and electrically connect the conductors together. An anti-fuse may also be enabled by directing a laser beam at a predetermined portion of the anti-fuse (i.e. the dielectric) to electrically connect the conductors together.
Still another type of programmable link is known as a laser programmable link. As an example, a segment of a conductive line (i.e. polysilicon) located on the surface of a chip can be melted through at a predetermined location using a laser beam. This is also sometimes referred to as laser break-link programming.
In accordance with the present invention, a semiconductor die can be constructed with programmable links arranged in a circuit for identifying the die. Such a circuit is permanent and electronically accessible.
Accordingly, it is an object of the present invention to provide a method for identifying a semiconductor die utilizing a programmable integrated circuit which can be easily accessed during manufacture and throughout the life of a semiconductor die. It is a further object of the present invention to provide an integrated circuit which includes programmable links that may be selectively activated to create a code for identifying a semiconductor die. It is yet another object of the present invention to provide a programmable integrated circuit for identifying a semiconductor die that is adaptable to large scale semiconductor manufacture.